JSFiddle - React, Tailwind, and code Playground

JavaScript

function findFirstKeyByValue(obj, val) {
    for (var key in obj) {
        if (obj.hasOwnProperty(key) && obj[key] === val) {
            return key;
        }
    }
    return null;
}

arr = {
"a": "b",
"c": "d",
"e": "f"
};

uri = "d";

alert(findFirstKeyByValue(arr, uri))